During reproduction processes such as electrophotography, it is necessary to charge a photoconductive surface of a photoreceptor member to a uniform level, which charge will subsequently be selectively dissipated by exposure to light. The non-discharged portions retain their charge in the form of a latent image on the photoconductive surface, and when subsequently brought into contact with toner material, will retain toner on the surface of the photoreceptor in the areas where the charge has not been dissipated. At a later time, a final support member, such as paper, transparencies, etc. may be brought into contact with the photoconductive surface, and a charge applied to the backside of the support material will attract toner on the photoconductive surface to the support material. The toner on the support material may then be fused thereto to provide a permanent image on the support material.
In the past, the primary method of charging a photoconductive surface of a photoreceptor member in an electrophotographic device to a uniform level has been to provide a corotron charging system including a corona discharging wire or needle arrangement closely adjacent to the photoreceptor and extending transversely across its path of travel in conjunction with a high voltage power supply generally operating at a level in the range of approximately .+-.5000 to 8000 volts. This arrangement, while commonly used, has significant drawbacks in that it requires an expensive power supply, creates significant amounts of ozone deleterious to the photoreceptor surface, and results in an undesirable high voltage potential across an air gap of about 0.5 inches which may be hazardous to users of the device. In a similar manner, contacting roller members may be used to apply a charge to the photoreceptor, as shown by U.S. Pat. Nos. 3,626,260, to Kimura et al and 4,380,384 to Ueno et al, IBM Technical Disclosure Bulletin, "Apparatus for Charging Xerographic Plates" by Randolph and Brookman, Vol. 8, No. 12, page 1729, (May 1966), and Proceedings of the National Electronics Conference, "High Speed Printing of Cathode Ray Tube Information by Electrostatic Photography Techniques" by Straughan and Mayer, Vol. 13, page 959, (1958). Such contacting roller arrangements must also be driven at relatively high voltages. Significant cost advantages may be obtainable if expensive power supply and ozone suppression requirements could be eliminated.
A potential substitute for such an arrangement is induction roll charging. Induction roll charging is known, for example, as shown in U.S. Pat. Nos. 3,684,364 to Schmidlin, 3,172,024 to Gundlach or 3,084,061 to Hall, in which a bias roller charging member is arranged in rolling engagement with a photoreceptor surface, applying a field to the photoconductor whereby charge is induced on the photoconductive surface by causing a migration of charge carriers from an injecting interface to an area adjacent the photoreceptor surface. Such a charging arrangement allows significant reductions in the voltage requirements of the system, to voltages levels on the order of -100 to -500 volts, and produce essentially no ozone. Additionally, since the charging operation of the bias roller arrangement is to induce current to flow from a hole injecting substrate layer underlying the photoconductive surface, there is only a minimal amount of leakage current drawn from the bias roller power supply. A bias roller charging arrangement may offer additional significant advantages over corotron charging methods if the arrangement can be provided with an alternating current power source with preferably line voltage output levels and operating frequency. However, problems in the use of an alternating current (A.C.) power source, described in Oliphant U.S. Pat. No. 3,147,415, including strobing or banding of the charge level induced along the photoconductive surface, create problems in the implementation of induction roll charging.